1. Field of the Invention
The present invention relates to a heat-processing furnace and a manufacturing method thereof.
2. Related Art
In a manufacturing process of a semiconductor device, various heat-processing apparatuses are used to subject a semiconductor wafer as an object to be processed to an oxidation process, a diffusion process, and a CVD (Chemical Vapor Deposition) process. A general heat-processing apparatus includes a heat-processing furnace formed of: a processing vessel (reaction tube) in which a semiconductor wafer is housed and heat-processed; a heating resistor disposed around the processing vessel; and a heat insulating member disposed around the heating resistor. The heating resistor is arranged on an inner wall surface of the heat insulating member through a support member.
In the case of a heat-processing apparatus capable of performing a batch process, a helical heater line arranged along an inner wall surface of a cylindrical heat insulating member is used as the heating resistor. Thus, an inside of a furnace can be heated at a high temperature such as 800° C. to 1000° C. As the heat insulating member, there is used a heat insulating member made by baking a heat insulating material such as ceramic fibers into a cylindrical shape. Thus, a heat quantity taken away as a radiant heat and a conductive heat can be reduced to promote an efficient heating operation. As the support member, a support member made of, e.g., ceramics is used to support the heater line at predetermined pitches to allow a thermal expansion and a thermal shrinkage of the heater line.
In the above heat-processing furnace, the heater line is formed into a helical shape, and is supported with a clearance between the heater line and the heat insulating member such that the heater line can thermally expand and thermally shrink. However, use of the heating line under a high temperature invites a creep strain, so that a length of the heating line is gradually increased. In addition, the heater line thermally expands upon heating. Further, a certain heater line is rapidly cooled by blowing air thereto so as to lower the temperature. When the temperature of the heater line is repeatedly elevated and lowered, the heater line is deformed. Then, there is a possibility that the heater line is broken because of a short circuit formed between a part of the heater line and an adjacent part thereof.
Particularly in a vertical heat-processing furnace, because of repeated thermal expansions and thermal shrinkages of a heater line caused by repeated fluctuation in temperature, the heater line is gradually, slightly moved downward in a support member by gravitation. Since the amount of movement is accumulated at a lowermost turn, a winding diameter of the heater line is increased by the movement accumulation. When the heating line reaches an inner surface of the heat insulating member, since the heater line cannot expand outward any more, the heater line is vertically deformed. As a result, there is a possibility that the heater line is broken because of a short circuit formed between a part of the heater line and an adjacent part thereof.
In order to solve this problem, i.e., in order to prevent accumulation of elongation of a heater line on one side, which is caused by a creep or a thermal expansion of the heater line, there has been proposed that a rod-like fixing member projecting radially outward from a furnace is disposed on an outside part of a heating resistor by welding, and an end of the fixing member is buried in a heat insulating member to be fixed therein (see, JP10-233277A).
However, since the fixing member is merely joined by welding to the outside part of the heating resistor, not only the joint is exposed to a high temperature, but also a stress tends to be concentrated on the joint when the heating resistor thermally expands and shrinks, whereby durability may be degraded (life duration is shortened). Further, since the fixing member has a rod-like shape, the fixing member is easily escaped from the heat insulating member, which results in inferior sustainability. Namely, it may be difficult to maintain a fixing performance of the heating resistor to thereby degrade durability.
The present invention has been made in view of the foregoing circumstances. The object of the present invention is to provide a heat-processing furnace and a manufacturing method thereof having an improved durability as compared with a conventional fixing member of a heating resistor.